1. Field of the Invention
The present invention generally relates to a scroll type compressor and in particular to a scroll type compressor used in an air conditioning system of a vehicle.
2. Description of the Related Art
Typical components of a conventional scroll type compressor include a fixed scroll formed with a spiral element provided on the surface of a fixed end plate and a movable scroll formed with a spiral element provided on the surface of a movable end plate. Both spiral elements are interfit and disposed in a housing such that one spiral element's side wall contacts various portions of the other spiral element's side wall. As a result, fluid pockets form between the two spiral elements. A suction chamber, defined between the interfit spiral elements and the inner wall of the housing, supplies refrigerant gas to the fluid pockets when the movable scroll rotates. As the fluid pockets move toward the center of the spiral elements, the volumes of the fluid pockets decrease, and in that way, the scroll elements compress the refrigerant gas. The compressed refrigerant gas is then discharged into a discharge chamber located in the aforementioned housing via a discharge port formed in the center portion of the fixed scroll's end plate.
To reduce the weight of these scroll type compressors, the fixed scroll can be made from a light weight metal, such as aluminum or from an aluminum-nickel alloy. The compressor's housing can likewise be made from a light weight metal in order to achieve weight reduction. Japanese Unexamined Patent Publication No. 61-38189 discloses such a housing and fixed scroll formed as separate components. Even further reduction in weight can be accomplished by decreasing the overall size of the compressor, as well as by integrating the housing and fixed scroll into a single component, as disclosed, for example, in Japanese Unexamined Patent Publication No. 3-134287 and Japanese Unexamined Utility Model Publication No. 5-1882.
Scroll type compressors, having separately formed housing and fixed scroll components, enjoy a high degree of design freedom, by being able to use a large cross-sectional area for the refrigerant gas to pass from the suction chamber to the fluid pockets. This helps to assure proper displacement of refrigerant gas from the suction chamber into the fluid pockets.
In order to enhance the strength of the fixed spiral element, in the case where the fixed scroll is integrally formed with the housing, the outer tip portion of the fixed spiral element can be made thicker, relative to other portions, with the thick portion integrally coupled to the inner peripheral surface of the housing. More specifically, as shown in FIG. 13, the outer tip portion of a fixed spiral element 1b, formed integrally with a cylindrical housing 1d, is continuous along the inner wall of the housing 1d, forming a connecting section 1e. A movable scroll 9, which engages the fixed spiral element 1b and the connecting section 1e, has a disk-like end plate 9a and a spiral element 9b formed integrally with the end plate 9a. When the end plate 9a slides in contact with a sealing surface S1, between the fixed spiral element 1b and the connecting section 1e, fluid pockets P between both spiral elements 1b and 9b are effectively sealed.
During the revolution of movable scroll 9, when the outer tip portion, 9e, of the movable spiral element 9b, comes closest to the inner peripheral surface, S3, the outer peripheral portion of the end plate 9a, indicated in FIG. 13 by long and dashed lines also comes closest the inner peripheral surface S3. Consequently, fluid communication occurring at the beginning of the suction stroke from the suction chamber 12 to a fluid pocket Ps is for the most part blocked. The blockage creates a pressure differential between the space 12 and the fluid pocket Ps on opposite sides of the movable spiral element 9b. The action of this differential pressure produces a counter-force to the smooth orbital movement of the movable scroll 9. This counter-force tends not only to impair the smooth orbital movement of the movable scroll 9, but also to degrade the sealing contact of the fluid pocket Ps with the scroll elements and the end plates. The net result of the aforementioned blockage is to produce an increase in wear on the sliding portions of both spiral elements and, consequently, to decrease the compression efficiency of the scroll type compressor.